[PATCH] arm64: Use correct method to calculate nomap region boundaries

[Will Deacon]

On Mon, Dec 06, 2021 at 12:46:27PM +0800, Huacai Chen wrote:
> On Thu, Dec 2, 2021 at 6:08 PM Will Deacon <will at kernel.org> wrote:
> > On Fri, Oct 22, 2021 at 03:06:46PM +0800, Huacai Chen wrote:
> > > Nomap regions are treated as "reserved". When region boundaries are not
> > > page aligned, we usually increase the "reserved" regions rather than
> > > decrease them. So, we should use memblock_region_reserved_base_pfn()/
> > > memblock_region_reserved_end_pfn() instead of memblock_region_memory_
> > > base_pfn()/memblock_region_memory_base_pfn() to calculate boundaries.
> > >
> > > Signed-off-by: Huacai Chen <chenhuacai at loongson.cn>
> > > ---
> > >  arch/arm64/kernel/setup.c | 6 ++++--
> > >  1 file changed, 4 insertions(+), 2 deletions(-)
> > >
> > > diff --git a/arch/arm64/kernel/setup.c b/arch/arm64/kernel/setup.c
> > > index be5f85b0a24d..1e86d4c5ef8c 100644
> > > --- a/arch/arm64/kernel/setup.c
> > > +++ b/arch/arm64/kernel/setup.c
> > > @@ -232,12 +232,14 @@ static void __init request_standard_resources(void)
> > >               if (memblock_is_nomap(region)) {
> > >                       res->name  = "reserved";
> > >                       res->flags = IORESOURCE_MEM;
> > > +                     res->start = __pfn_to_phys(memblock_region_reserved_base_pfn(region));
> > > +                     res->end = __pfn_to_phys(memblock_region_reserved_end_pfn(region)) - 1;
> > >               } else {
> > >                       res->name  = "System RAM";
> > >                       res->flags = IORESOURCE_SYSTEM_RAM | IORESOURCE_BUSY;
> > > +                     res->start = __pfn_to_phys(memblock_region_memory_base_pfn(region));
> > > +                     res->end = __pfn_to_phys(memblock_region_memory_end_pfn(region)) - 1;
> > >               }
> > > -             res->start = __pfn_to_phys(memblock_region_memory_base_pfn(region));
> > > -             res->end = __pfn_to_phys(memblock_region_memory_end_pfn(region)) - 1;
> >
> > Under which circumstances would the nomap regions not be page-aligned? That
> > sounds like something we should prevent, rather than work around here.
> 
> In this call path:
> acpi_table_upgrade --> arch_reserve_mem_area --> memblock_mark_nomap
> The nomap region is not page-aligned.

Fair enough, then I think this patch is probably doing the right thing.
However, Ard and Mark had some concerns about the new behaviour wrt
adjacent nomap regions where the page containing the overlap would be
reported twice. Is this a problem?

Will